1. Field of the Invention
This invention relates to a method for forming a phase shift mask which can be used during a lithographic process, and more particularly to a method for forming a self-aligned phase shift layer pattern by a Chrome (Cr) pattern which is formed on opposite side of a transparent glass.
2. Information Disclosure Statement
As is generally known, in order to form a pattern on the surface of a wafer, a photo-mask of a Cr pattern which is formed at a predetermined portion of a transparent glass by irradiating an electron beam is used in the lithographic process. However, since a highly integrated semiconductor device has been manufactured, high resolutions capable of forming a microscopic pattern have been required.
Therefore, in order to manufacture the microscopic pattern on the surface of the wafer with high resolution according to the conventional method, a phase shift mask including a phase shift layer pattern with high transmission factor overlapped on a Cr pattern has been manufactured. However, the phase shift pattern and Cr pattern is not accurately overlapped so that it is difficult to form a submicron pattern of the semiconductor device.
With reference to FIG. 1A through FIG. 1C, the conventional method for forming the phase shift mask will now be described.
FIG. 1A is a cross-sectional view illustrating a Cr pattern 2 formed on a transparent glass 1 by irradiating an electron beam.
As shown in FIG. 1B, after a phase shift layer 3 comprising SiO.sub.2 or SOG is entirely formed on the transparent glass 1 and the Cr pattern 2, a resist layer (not illustrated) is coated and a mask 4 is positioned on the resist layer in order to form a phase shift layer pattern.
As shown in FIG. 1C, the resist layer, which the mask 4 is not positioned, is exposed by irradiating the electron beam and a resist pattern (not illustrated) is formed by removing only the resist layer which is not exposed by irradiating the election beam. Thereafter phase shift layer pattern 3' is formed by removing the phase shift phase layer 3 exposed by the resist pattern and the resist pattern is removed. Whereby a phase shift mask comprising the phase shift layer pattern 3' is overlapped the Cr pattern 2 is made.
In case of the phase shift pattern 3' is ideally manufactured, a wanted pattern on the surface of the wafer (not illustrated) with high resolution is made because the phase shift effect of the phase shift mask is accurately obtained during the photo-lithographic process. However, when a phase shift layer pattern 3" (shown as the dotted line) and the Cr pattern 2 are manufactured with overlapping error, the phase shift effect of the phase shift mask is not accurately obtained so that the wanted pattern is not achieved during the photo-lithographic process. Therefore, in order to form the pattern on the surface of the wafer with high resolution on the wafer, the overlapping error between both patterns 3', 2 should be minimized.
However, the overlapping accuracy of the phase shift layer pattern on the Cr pattern is not easily increased according to the conventional method since there are many factors to misalign them such as using another mask for forming said phase shift layer pattern, etc. In general, it is very troublesome procedures to accurately align the another mask to Cr pattern during a lithographic process.